One other thing that I am surprised that K9YC has not mentioned. In the G5RV, the 450 ohm ladder line (don’t use 300 ohm line) connected directly to the coax. That sets up a situation where return currents may be flowing on the outside of the coax shield. Which is really bad. The coax needs to have a choke at that point. You can wind the coax through a fairly large toroid to do the job (as many as you can put on the toroid). The best source of information for this is K9YC’s site - he has a Choke Cookbook that is a must read for this topic. Jim spent many hours doing extensive research on this very topic, and has published the results of all that research. And, it is free! See: http://audiosystemsgroup.com/2018Cookbook-Pacificon2021.pdf While you are at it, you might look over the various presentations that Jim has made available. The main site is at: http://audiosystemsgroup.com/publish.htm And, Jim is here to answer our questions. He is one of the guys I miss since moving away from 6-land.
73, Jack, W6FB > On Jul 19, 2025, at 7:11 PM, Jack Brindle via Elecraft > <[email protected]> wrote: > > Ladder-line? THAT is an important piece of information. Open wire line is > great. It is very hard to get these days. Almost as great is ladder line. I > use a lot of it. It has one pretty big problem - when it gets wet, its > impedance characteristics change. When that happens you will need to retune. > I say this with a lot of experience. In this case it is not the ATU, but > definitely the ladder line. > > I will say for the second time, there are NO reed relays in the KAT500 or > KPA500. I am very familiar with those relays. They can carry lots of power, > but do not take kindly to being hot-switched. My KPA500 code makes sure they > are not hot-switched, and I know the code in the KAT500 performs the same > way. When we need to break the PTT line to the amplifier, we use a smaller > relay that handles the very low current signaling of the PTT line. And yes, > we do negate the PTT/Key line if SWR gets out of range. > > Third, you should be using about 20 watts to tune the KAT500. It performs > best at that level. In any case, be sure to read the KAt500 manual - it tells > you the correct specs and how you should handle things. Also, while it is a > good idea, there is no need to tune the KAT with the KPA500 in STBY. The > KAT500 always opens the PTT line when a tune is requested, which directly > puts the KPA into low-power mode where it is not amplifying. This assumes, of > course, that you are using the proper control cables to connect the > transceiver to the KAT500, then to the KPA500. Again, read and follow the > manuals. > > You _could_ have a problem with the KAT500s, but if both behave the same, it > is probably not them. As much as we hate going through our antenna systems, > that is a must in this case. You really don’t want to send the KATs back to > Watsonville only to have them returned with no trouble found along with a > repair and shipping bill. Take the time to make sure your antennas really are > in good shape. We get lots of reports on this one, and pretty much every time > the ham ends up finding something deficient in the antenna system. Just > because something works well at 100 watts, does not mean it will at 500. And > yes, pretty much everyone who upgrades to an amplifier (including me) found > this out the hard way. I learned the lesson and fixed my antennas properly, > and still use the very first KPA500 many years after we first powered it up. > It is a great amplifier! > > 73, > Jack, W6FB > KPA500 firmware developer and engineer of other devices… > > >> On Jul 19, 2025, at 11:35 AM, dave ingebright via Elecraft >> <[email protected]> wrote: >> >> Jim, Thanks for your query. I'm tuning at less than 10W, KPA amp always in >> STBY. Sometimes the tuner finds a better match at a little more power (25-75 >> Watts); someone else mentioned that, too. >> But again, yesterday, it found the solution (Multiband ladder-fed G5RV at >> 40') 14Mhz, and everything was fine during the first part of the FT8 QSO, >> and then the tuner went to a high SWR fault for no apparent reason. >> I reset it, and it was fine for the rest of the operating session. It >> doesn't matter what band or what power. Remember, I have two of these doing >> the same thing. >> I still bet there are a couple of little reed relays with pitted contacts in >> the auto tuner. I am sure a lot of us have wondered how they get away with >> using those in a ~500W high-voltage environment. I will call the tech line, >> but wondered if any of you on this reflector have had this problem >> //dave >> WB7ELY >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:[email protected] >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html >> Message delivered to [email protected] > > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > Message delivered to [email protected] ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
